IBM Spectrum Virtualize overview

The IBM Spectrum Virtualize™ system combines software and hardware into a comprehensive, modular appliance that provides symmetric virtualization. IBM Spectrum Virtualize software providessymmetric virtualization.

Symmetric virtualization is achieved by creating a pool of managed disks (MDisks) from the attached storage systems and optional SAS expansion enclosures.Volumes can be created in a pool for use by attached host systems. System administrators can view and access a common pool of storage on the storage area network (SAN). or local area network (LAN). This functionality helps administrators to use storage resources more efficiently and provides a common base for advanced functions.

A SAN is a high-speed Fibre Channel network that connects host systems and storage devices. A LAN is a high-speed Ethernet network that connects host systems and storage devices. In a SAN and LAN, a host system can be connected to a storage device across the network. The connections are made through units such as routers and switches. The area of the network that contains these units is known as the fabric of the network.

IBM Spectrum Virtualize software

IBM Spectrum Virtualize software is part of the IBM Spectrum Storage™ family.

IBM Spectrum Virtualize is a key member of the IBM Spectrum Storage portfolio. It is a highly flexible storage solution that enables rapid deployment of block storage services for new and traditional workloads, on-premises, off-premises and in a combination of both. Designed to help enable cloud environments, it is based on the proven technology. For more information about the IBM Spectrum Storage portfolio, see the following website.
The software provides these functions for the host systems that attach to the system:
  • Creates a single pool of storage
  • Provides logical unit virtualization
  • Manages logical volumes
The system also provides the following functions:
  • Large scalable cache
  • Copy Services:
    • IBM® FlashCopy® (point-in-time copy) function, including thin-provisioned FlashCopy to make multiple targets affordable
    • IBM HyperSwap® (active-active copy) function
    • Metro Mirror (synchronous copy)
    • Global Mirror (asynchronous copy)
    • Data migration
  • Space management:
    • IBM Easy Tier® function to migrate the most frequently used data to higher-performance storage
    • Metering of service quality when combined with IBM Spectrum Control Base Edition. For information, refer to the IBM Spectrum Control Base Edition documentation.
    • Thin-provisioned logical volumes
    • Compressed volumes to consolidate storage
Figure 1 shows hosts, system nodes, and RAID storage systems connected to a SAN fabric. The redundant SAN fabric comprises a fault-tolerant arrangement of two or more counterpart SANs that provide alternative paths for each SAN-attached device.
Figure 1. Example of a system in a fabric
This figure shows an overview of a system in a SAN fabric.


System nodes present volumes to the hosts. Most of the advanced system functions are defined on volumes. These volumes are created from managed disks (MDisks) that are presented by the RAID storage systems. The volumes can also be created by arrays that are provided by flash drives in an expansion enclosure. All data transfer occurs through the system node, which is described as symmetric virtualization.

Figure 2 shows the data flow across the fabric.

Figure 2. Data flow in a system
This figure shows an overview of data flow in an IBM SAN Volume Controller system

The nodes in a system are arranged into pairs that are known as I/O groups. A single pair is responsible for serving I/O on a volume. Because a volume is served by two nodes, no loss of availability occurs if one node fails or is taken offline. The Asymmetric Logical Unit Access (ALUA) features of SCSI are used to disable the I/O for a node before it is taken offline or when a volume cannot be accessed via that node.

Volume types

You can create the following types of volumes on the system:
  • Basic volumes, where a single copy of the volume is cached in one I/O group. Basic volumes can be established in any system topology; however, Figure 3 shows a standard system topology.
    Figure 3. Example of a basic volume
    This figure shows an example of a basic volume.
  • Mirrored volumes, where copies of the volume can either be in the same storage pool or in different storage pools. As Figure 4 shows, the volume is cached in a single I/O group. Typically, mirrored volumes are established in a standard system topology.
    Figure 4. Example of mirrored volumes
    This figure shows an example of mirrored volumes.
  • HyperSwap volumes, where copies of a single volume are in different storage pools that are on different sites. The volume is cached in two I/O groups that are on different sites, as Figure 5 shows. These volumes can be created only when the system topology is HyperSwap.
    Figure 5. Example of HyperSwap volumes
    This figure shows an example of HyperSwap volumes.

System topology

The topology property of a system can be set to one of the following states:
  • Standard topology, where all nodes in the system are at the same site.
    Figure 6. Example of a standard system topology
    This figure shows an example of a standard system topology
  • Stretched topology, where each node of an I/O group is at a different site. When one site is not available, access to a volume can continue but with reduced performance.
    Figure 7. Example of a stretched system topology
    This figure shows an example of a stretched system topology
  • HyperSwap topology, where the system consists of at least two I/O groups. Each I/O group is at a different site. Both nodes of an I/O group are at the same site. A volume can be active on two I/O groups so that it can immediately be accessed by the other site when a site is not available.
    Figure 8. Example of a HyperSwap system topology
    This figure shows an example of a HyperSwap system topology

System management

A system is composed of individual nodes that present a single point of control for system management and service. System management and error reporting are provided through an Ethernet interface to one of the nodes in the system, which is called the configuration node. The configuration node runs a web server and provides a command-line interface (CLI). Any node in the system can be the configuration node. If the current configuration node fails, a new configuration node is selected from the remaining nodes. Each node also provides a command-line interface and web interface for initiating hardware service actions.

Fabric types

I/O operations between hosts and system nodes and between the nodes and arrays use the SCSI standard. The nodes communicate with each other through private SCSI commands.

Table 1 shows the fabric type that can be used for communicating between hosts, nodes, and RAID storage systems. These fabric types can be used at the same time.

Table 1. System communications types
Communications type Host to system nodes System nodes to storage system System nodes to system nodes
Fibre Channel SAN Yes Yes Yes
iSCSI (1 Gbps Ethernet or 10 Gbps Ethernet) Yes Yes No

IBM Spectrum Virtualize node

In a clustered system, a node is an individual server upon which the IBM Spectrum Virtualize software runs.

The nodes are always installed in pairs; a minimum of one pair and a maximum of four pairs of nodes constitute a system. Each pair of nodes is known as an I/O group.

I/O groups take the storage that is presented to the SAN by the storage systems as MDisks. The storage is then transformed into logical disks (volumes) that are used by applications on the hosts. A node is in only one I/O group and provides access to the volumes in that I/O group.

I/O operations between hosts and system nodes and between the nodes and arrays use the SCSI standard. The nodes communicate with each other through private SCSI commands.